Hybrid electric vehicles have become much more widespread over the last decade, going from a niche solution to an established technology. The limits of electrification are being explored enthusiastically in industry, with electric motors and actuators being prototyped and perfected in on-road vehicles such as cars and trucks, as well as off-road vehicles such as farming, construction, and mining equipment. Once known almost exclusively for their fuel saving advantage over combustion only solutions, hybrid electric vehicles are now also recognized for their improved performance. The resulting abundance of electrical energy on vehicles has opened up new opportunities for improved performance by replacing slower and less efficient hydraulic and mechanical systems with faster, quieter, tighter controlled, and more efficient electric machines and actuators.
Two forms dominate the hybrid electric vehicle market: parallel and series hybrids. The topology of a parallel hybrid is such that motion can be achieved through sole use of an engine, sole use of an electric motor, or combined use of both an engine and an electric motor. In a series hybrid, an engine is used to spin an electric machine that generates electricity, which (with power electronics) can then be used by a second electric machine to provide motion. The series hybrid topology allows elimination of the transmission from the vehicle, improving efficiency and smoothness of operation as well as reduction in complexity and audible noise. Both the series and parallel hybrids often also have batteries in the system for electrical energy storage.
Hybrid electric systems are operated through the use of power electronics typically referred to as inverters (or converters). Control loops are a critical part of the inverters in known systems, allowing commands for torque, speed, and voltage to be satisfied. Furthermore, the accuracy and responsiveness of these control loops are an important part of what gives electrification an edge over its more seasoned hydraulic and mechanical counterparts. To achieve this higher level of performance in known systems, robust control schemes must be utilized. Additionally, commercialization of these systems requires cost reduction, which can be accomplished through sensor replacement methodologies (observers).
Traditional voltage controllers are often constructed with only proportional and integral control. This topology is prone to poor dynamic performance and disturbance rejection.